Conventionally, as shown in FIG. 10, this type of robot is disposed in the periphery of a working machine 50 and is provided with a plurality of arms 52 which are connected by a plurality of revolute joints 51. A hand 53 mounted on the front most arm 52 is regulated to trace a plurality of points which are preliminarily taught. The hand 53 is provided with a gripping element such as a vacuum cup 54 and a sensor 56 which detects a work 55 coming into contact with the vacuum cup 54 as the hand 53 is descended. To load the work 55 to the working machine 50, a work searching operation is carried out in which the ha nd 53 is firstly shifted to a position which is located a predetermined distance right above the works 55 stacked on a sheet stack base 57. The hand 53 is then descended slowly until the sensor 56 detects the vacuum cup 54 coming into contact with the work 55 and then the descending of the hand 53 is stopped. When the descending operation of the arm 52 is stopped upon detection of the work 55, the operation is succeeded by a next operation such as a transferring of the work 55 to the working machine 50. On the other hand, in case that a work 58 after machining is to be stacked on a product stack base 59 one after another, the above-mentioned operation is carried out substantially in the same manner but in a reverse mode. Namely, the sensor detects the work 58 gripped by the vacuum cup 54 coming into contact with the product stack base 59 and evacuates or releases the suction force of the vacuum cup 54 thus allowing the vacuum cup 54 to advance to a transferring of a next work 58 to the product stack base 59. In FIG. 10, a numeral 60 indicates a control panel.
In the above-mentioned method, the arm 52 is slowly descended from the highest position which is higher than the uppermost stacked work. Accordingly, in case that the works 55, 58 which are stacked on the stack base 57,59 are small in number, time is wasted and a cycle time is elongated. The task of the present invention substantially lies in making the cycle time short employing the above-mentioned conventional apparatus and method.